Our previous studies on the fine structure of biochemically-dissected human sperm nuclei-revealed the presence of chromatin beads about 300-750 Angstrom units in diameter interlaced by 20-30 Angstrom units fibers. In these proposed studies, the organization of human sperm chromatin will be invesigated by digesting the chromatin with nucleases and proteases and then analyzing the products of digestion by sucrose density gradient sedimentation and electron microscopy. In addition, the chromatin structure will be probed by photochemically crosslinking the DNA in situ at protein constraint-free regions and then determining by electron microscope mapping of the isolated DNA where the crosslinks occur. The data generated by these experiments should help reveal the protein-DNA architecture of sperm chromatin. As a second part of this study, a recently discovered sperm nuclear DNA synthesizing complex (DNA polymerase) that may play an inportant role in the early events of fertilization and/or embryogenesis will be further characterized. Attempts will be made to localize this complex in sperm heads by: (a) Electron microscope auroradiography of sperm heads labeled in situ with 125I by an endogenous DNA synthesizing reaction, and (b) Thin section electron microscopy using ferritin-tagged antibody against purified baboon endogenous virus DNA polymerase which cross reacts with human sperm DNA polymerase; confirmation of its presence plus specific localization may aid in ascertaining its function. These investigations are expected to provide fundamental information on the structure of sperm chromation that is considered essential to a better understanding of the mechanisms involved in sperm nucleus to pronucleus transition and male-genome expression.